It should be noted that this section is intended to introduce various aspects of art to the reader, which may be related to various aspects of the present invention that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Due to the rapid development of wireless communication technologies, video communication using video phones, video streaming and video broadcasting is becoming more and more popular. In such kind of communication process, packets of compressed media data may be transmitted over unstable networks, during which period spatial and temporal distortions may be introduced by either data loss in compression or packet loss in transmission. Bit rate adaptation techniques and packet loss in a network could be the origin of a perceived video quality degradation. At the source coding stage, temporal down-sampling is one of the techniques employed for bit rate adaptation, in which the sequences undergoes a frame dropping operation that affects the motion continuity of the video.
A perceptual jitter is a common video quality degradation caused by frame loss. Generally speaking, the perceptual jitter is a kind of temporal artifact perceived in the case that one or more consecutive frames in a video frame sequence are lost during video streaming and then at the subsequent displaying stage are substituted by the last correctly received frame. FIG. 1 is an exemplary diagram showing a perceptual jitter caused by frame loss, such as frame dropping or discarding. The frame loss process and its influence on video quality are shown in FIG. 1. The line in FIG. 1 represents the moving trajectory of an object, where the X-axis is time and the Y-axis is the object position. The frames between time B0 and time B are dropped. In this case, since the last correctly received frame at the time B0 will be displayed till a new frame is correctly received at the time B, the displayed object will keep still during this period and then jump immediately to a new position. If this period is relative short and the object movement is slight, a viewer is able to guess what the object is doing and will not perceive a motion discontinuity. Otherwise, human brain of the viewer will fail to conceal the “motion discontinuity” phenomenon, which will make the viewer recognize this temporal artifact.
Some studies have been done to evaluate the perceptual impact of temporal degradations caused by perceptual jitters. Based on specific subjective tests described in the prior art1, it was concluded that a perceptual quality decreases with the increase of the number of dropped frames. The above conclusion is extended by the study made by the prior art2 to a conclusion that perceptual impact is highly content dependent. The conclusion in the prior art3 is similar to the above two prior arts but specifies that the depended content factor to be motion activity—video with low motion activity does not suffer in perceptual quality quite as much in the presence of jitters as does high motion activity video. A quantitative model is also proposed based on the above assumptions.
However there is no systematic evaluation scheme available for perceptual jitter yet.